Judgment Day – The human race is dying off. The rivers are drying up, crops are failing and the soil barren. The atmosphere is so thick with pollutants and dust that the sun no longer penetrates to the surface of the earth, cutting off the main energy source of the biosphere. Man is doomed, the world an inhospitable environment. There is no food, no water and the very air is a deadly poison. Death is the only fate for the race…. but what if it didn’t have to be?
What if we could preserve the race in suspended animation to return only when the environment has recovered and can again support life? Even if this takes centuries to happen and in the mean time you are exposed to unbearable heat, toxic chemicals, drought, starvation, nuclear radiation exposure and the wear and tear of time as the years pass. Wishful thinking. This is impossible and can never happen. Well, maybe not for us human beings but for two gram positive genera of bacteria this is a reality. Both the Clostridium and Bacillus genera have the amazing ability to ensure the survival of their kind by preserving their DNA in an impenetrable and almost indestructible capsule called an endospore.
This last resort is only used when absolutely necessary, after all other attempts at survival are unsuccessful. When a bacterium can no longer survive in an environment, it copies it’s DNA and creates the enduring endospore to protect it. This DNA can survive for years until conditions are favourable outside again. It is a sacrificial process whereby if the bacterium does begin the process of sporulation, it will die in the process. The organisms DNA is preserved however, ensuring the survival of the strain. The resulting germinated bacterium is merely a clone of the original.
With Bacilli being aerobic and Clostridium being anaerobic, these spores are produced by a wide range of bacteria. A major problem with endospores, in regard to everyday life for humans, is in the preservation of food. Scientists have had to develop ways of destroying endospores present on food or ways of ensuring they cannot germinate. Unfortunately, the majority of endospore forming bacteria are pathogens. Therefore, the consumption of endospores creates a health risk as there is no better environment to bring about germination than the warm, moist intestines of a mammalian body. Infant botulism is a prime example of this. The endospores of Clostridium botulinum can be found in honey where they are unable to germinate due to the excessive sugar levels. If an adult consumes the spores in the honey they are unaffected because the spores cannot tolerate the strong acid in the stomach and the abundance of intestinal flora already present. If an infant under twelve months were to eat the honey however, the spores would find themselves in the ideal environment for germination as the stomach acid is weaker and the natural flora not yet established. Infant botulism can lead to respiratory failure and even death if not treated. Another high profile case of the dangers of this property of endospores than the anthrax scare in the USA in 2001. There was widespread panic when endospores of Bacillus anthracis were posted in envelopes causing several deaths as the inhaled spores quickly germinated and led to respiratory failure. One worry is that as well as Bacillus anthricis, many of the endospore producing bacteria can be used in biological warfare, including Clostridium Botulinum. The Bacillus anthracis also has a habit of lying dormant in soil for years until it unexpectedly germinates causing damage to livestock and humans alike.
It is widely accepted that some endospores can lay dormant for centuries waiting for conditions to become favourable again but there are cases of germination in the lab of endospores dating back several thousand years. Using the appropriate growth medium and aseptic technique scientists have been able to germinate Clostridium endospores found in the ancient tombs of Egypt. These tombs are approximately 4000 years old. Even more amazingly in 1995 the scientist Raúl Cano managed to germinate Bacillus sphaericus endospores found in the gut of a 30 million year old bee preserved in amber found in Dominica.
Whereas this is a significant scientific find, it does not quite signal the time for a real life Jurassic Park being made possible. It is the bacteria which come back but there is no DNA from other organisms which could be used to clone and grow new creatures (or old creatures as the case may be) even if the technology to do so was available. Unbelievably some scientists even claim to have germinated endospores that date back 250 million years though these claims have been met with scepticism and need to be verified (Vreeland, R. H., W. D. Rosenzweig, and D. W. Powers. 2000).
But what is an endospore? How can an organic specimen endure such rigours for such a long time with next to no metabolic activity and still maintain life to return and go on as normal? To answer this it’s important to understand the structure of an endospore. An endospore is a dry, non-dividing, metabolically almost inactive and dormant cell that is produced to preserve DNA by a moist, metabolically active, vegetative bacterial cell when it detects that it can no longer survive in its current environment.
It is amazing to think that a bacterium can become almost invincible in just eight hours, survive like that potentially for centuries and then return to normal in a mere hour.
With this remarkable resilience to survive almost any kind of attack added to the bacterial arsenal, is it any wonder they are found in almost any environment in the world. They can get energy from a variety of sources, through both heterotrophism and autotrophism. From the sun to volcanic springs at the bottom of the ocean under extreme pressure. They can live straight off raw chemicals in the case of chemotrophs. They can survive in the absence of oxygen, mutate almost on demand if they encounter any new problems. This includes new food sources and new powerful antibiotics. The bacteria can simply alter their DNA to resist the drug and to produce new enzymes that can break down the new food source. Is it any wonder bacteria are referred to as “The Ultimate Survivors”?